1. Field of the Invention
This invention relates to an image forming apparatus using the electrophotographic process, and particularly to an image forming apparatus such as a copier, a printer or a facsimile apparatus.
2. Related Background Art
In an image forming apparatus wherein a toner image is formed on a transfer material, and the transfer material is heated and pressurized by a fixing device to fix the toner image on the transfer material to thereby effect image formation, the thickness and kind of the transfer material are very important factors in determining the quality of image.
In a fixing device for fusing a toner and fixing it on a transfer material, the greater is the thickness of the transfer material, the greater becomes the quantity of heat taken away by the transfer material during fixing and the smaller becomes the quantity of heat for fusing the toner. Thereby, the toner is not sufficiently fused and bad fixing occurs. Particularly in an image forming apparatus wherein developers of plural colors are superposed one upon another to thereby form a color image, as compared with a case where a monochromatic image is formed, the quantity of the toners put on a transfer material is greatly increased and therefore, the difference in thickness between transfer materials greatly affects an image. Therefore, in an image forming apparatus for forming color images, as compared with an image forming apparatus for forming monochromatic images, particularly strict control is required of the temperature of the fixing device.
When the transfer material is light transmissive resin for an overhead projector (hereinafter referred to as "OHT"), an image must be formed under image forming conditions (a transfer high-voltage, a process speed, a fixing temperature, etc.) differing from the conditions in the case of plain paper in order to improve the light transmittance of the image. Also, regarding a case where the transfer material is glossy paper having gloss, it is necessary to form an image under image forming conditions differing from those in the case of plain paper.
Heretofore, when printing is to be effected on other transfer material than plain paper, a user has given the information of an operating panel or a computer from the operating panel or the computer to the image forming apparatus, has changed image forming conditions such as the transfer high-voltage during the printing operation, and the speed of the fixing device or the printing operation speed, and has performed the printing operation under image forming conditions optimum for the kind of the transfer material used.
Here, the printing operation according to the conventional art will be described with reference to the flowchart of FIG. 13.
First, whether the information of the kind of the transfer material (whether it is OHT or thick paper) has been given by the user is judged (601), and when there is no user's designation, the temperature of a fixing device is started to be attempered so as to become a print temperature for default (602), and the image forming conditions for default are set (603), and after the fixing device has been attempered to the print temperature (606), the printing operation is started (607).
On the other hand, when there is user's designation, the attempering of the temperature of the fixing device is started so that the fixing device may be attempered to a print temperature conforming to the thickness of the transfer material designated by the user (604), and after image forming conditions conforming to the thickness of the transfer material designated by the user are set (605), the fixing device waits until it is attempered to the set print temperature (606), and the printing operation is performed under the set image forming conditions (607).
However, in the printing operation as described above, when the user determines control conditions, i.e., image forming conditions, on the basis of the information of the transfer material inputted from the operating panel or the computer and performs the printing operation under the control conditions, the user may input wrong information and in that case, there has been the problem that a bad image is created.